Biostratigraphic events at the Barremian/Aptian boundary in the Betic Cordillera, southern Spain

This paper presents an analysis of the vertical distribution of ammonites and calcareous nannofossils throughout the uppermost Barremian-lowermost Aptian interval of pelagic sections in the External Zones of the Eerie Cordillera (southern Spain). We were able to identify all the standard ammonite zones in this interval and have established for the first time a direct calibration of calcareous nannofossil events against the ammonite zonation. The results confirm that the Baaemian/Aptian boundary, defined by the first appearance of Deshayesites, does not coincide with any other biostratigraphic event. Nonetheless, the sequence of events recorded in the studied sections provides alternative criteria on which to characterize this boundary with reasonable accuracy. A new nannofossil species (Micrantholithus stellatus sp. nov.) is also described. (C) 1997 Academic Press Limited.